Stable expression of MHC class I heavy chain/HLA-DO complexes at the plasma membrane

Major histocompatibility complex (MHC) class I and II molecules present antigenic fragments to the immune system. MHC-like chaperones, like HLA-DM, HLA-DO and tapasin support peptide loading. HLA class I heavy chains require association with beta 2-microglobulin and peptide for endoplasmic reticulum (ER) exit. Likewise, HLA-DO is only able to leave the ER by association to DM. Here we show that HLA-DO and free MHC class I heavy chains associate into a stable complex early during biosynthesis and are expressed at the plasma membrane as a complex. These DO/heavy chain complexes are found on DO-transfected cells and on low amounts on human B cells.